Gun barrel coated with tantalum



E. E. SLOWTER Filed May 16, 1946 E liwurd E. EIlEIW ILET XMWMMW Illll'lltlilllhflll I IWIILkI May 21, 1957 GUN BARREL COATED WITH TANTALUM GUNBARREL COATED WITH TANTALUM Edward E. Slowter, Columbus, Ohio, assignor,by mesne assignments, to Battelle Development Corporation, Columbus,Ohio, a corporation of Delaware Application May 16, 1946, Serial No.670,132

2 Claims. (CI. 42-76) This invention relates to methods for protectingsurfaces exposed to high frictional heat and to chemical erosion fromhot gases under great pressures, and to articles thus protected. Moreparticularly, the invention relates to gun barrels having improvederosion-resistant properties produced by the application of a coating ofa nonferrous metal to the bore surface thereof.

Many methods have been previously employed for treatment of the boresurface of firearm barrels in attempts to improve the erosion resistanceof the bore surface and, hence, the life of the gun barrel. Most ofthese methods have been directed to the improvement of erosionresistance of barrel steel itself by utilization of special steels, heattreatments, and surface treatments. While some advantages have beenobtained through such procedures, they have not solved the problem ofbore erosion. example, an electrolytically deposited layer of pure ironhas been attempted as a solution to this problem, but does not providesufi-lcient protection.

An object of this invention is to provide an 1 Side having a surfacewhich has greatly improved resistance to frictional erosion as well asto chemical erosion due to hot gases under great pressure.

Another object of this invention is to provide gun barrels having moresurfaces thereof treated to withstand chemical erosion and hightemperature effects.

A further object of this invention is to provide improved gun barrelshaving a coating of tantalum applied to the bore surface by a thermaldiffusion process.

The specific nature of the invention as well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown in the accompanying drawing wherein a longitudinalsectional view of a firearm barrel shows a coating of tantalum thermallydiffused over the surface of the bore.

Before referring to the drawing, it is to be understood that the termsused herein are for purposes of description and not of limitation. Forexample, gun barrel relates to any body having for its purpose thedirecting of a projectile from a firearm, regardless of size.

In the accompanying drawing, the particular embodiment of the inventionillustrated thereby represents a gun barrel 1 having a bore surface 2.The bore is preferably rifled by the provision of riding grooves 3-3.Over the interior bore surface a layer 4, a high-melting protectivemetal of the group consisting of tantalum, molybdenum, and tungsten, isapplied by any suitable method. While such a layer is shown as extendingthe entire length of the barrel, it will be apparent that improvederosion resistance could nevertheless be obtained if the layer 4 coveredmerely the portion of the bore adjacent the chamber of the barrel, sincethe most severe erosion conditions generally occur at this point.

Although several methods are available for applying the protectivemetallic layer 4 to the bore surface 2, or similar surfaces, it ispreferable to employ thermal deposition or diffusion methods in theapplication of such layers. A preferred embodiment of this inventionutilizes For 2,792,657 Patented May 21, 1957 the thermal deposition oftantalum on the bore surface of gun barrels by the diffusion process ofB. W. Gonser and E. E. Slowter as disclosed and claimed in the copendingapplication for United States Letters Patent Serial No. 629,630, filedNovember 19, 1945, now Patent Number 2,604,395.

in general, one particular application of this method comprises heatingthe surface to be coated and contacting said surface with a mixture ofhydrogen and a tantalum halide under such conditions as to causedeposition of substantially pure tantalum upon the heated surface. Thehydrogen gas is passed through various drying means to free it fromwater vapor and other deleterious gases before it is directed into afurnace containing a tantalum halide such as tantalum chloride. Thefurnace containing the tantalum halide is heated above the boiling pointof the tantalum halide employed which in no case need exceed 320 C., andis maintained below the decomposition temperature of this same halidewhen in contact with hydrogen, which is approximately 600 C. The rate atwhich the hydrogen gas is passed through the furnace containing thetantalum halide is preferably controlled so as to provide a. ratio ofabout l0 atoms of hydrogen to 1 atom of tantalum in the gas expelledtherefrom and passed into a second furnace in which is positioned thegun barrel to be coated. This excess amount of hydrogen is apparentlynecessary for the successful completion of the process and is just equalto twice the theoretical amount required to react with the halide in thetantalum salt.

The mixture of hydrogen and tantalum halide gas is passed through thebore of the gun barrel to be plated while the barrel is heated to suchtemperatures as to cause rapid decomposition of the tantalum halide whenin contact with the heated metal surface. While the temperature of thebore surface may range between 750 to 1300 C., optimum results have beenobtained at temperatures between 850 to 1150 C. When sufficient tantalumhas been deposited upon the bore surface to be coated, the heat isturned off from the first furnace containing the tantalum halide and theflow of gas therefrom is stopped before the removal of the treated gunbarrel from the second furnace.

One remarkable feature of this particular method of applying tantalum togun barrels is the fact that the tantalum apparently diffuses into thesurface layer of the bore so as to produce an iron-tantalum alloy. Forthis reason, it is impossible to measure the exact thickness of thetantalum layer applied, although estimates thereof can be made. It isbelieved that the tenacity with which the tantalum plate adheres to thebasis metal is due, at least in part, to the diffusion of tantalum intothe surface of the basis metal. The strong adherence of the plate to thebasis metal makes these tantalum coatings especially desirable for gunbarrels.

A steel test gun barrel was coated in the manner above described with alayer of tantalum approximately .001 inch thick while the bore surfacesthereof were heated to a temperature of about 930 C. After firing 400rounds from this barrel, only .008 gram of the barrel had been removeddue to erosion and other factors, and no heat checks were apparent. Gunbarrels of similar composition to that coated with tantalum, but havingno coating upon the bore surfaces thereof, lost between .15 and .16 gramin weight during the firing of 400 rounds under similar conditions, andafter the firing of 25 rounds heat checks appeared in every case. Amolybdenumcoated barrel lost only .097 gram after 400 rounds ofammunition had been fired therefrom and did not show heat checks untilrounds had been fired. Tungsten coatings have properties very similar totantalum and molybdenum and may be deposited thermally as abovedescribed. However, an adherent coating of tungsten to steel is moredifiicult to obtain than in the case of tantalum and molybdenum and itsusefulness, therefore, is somewhat limited.

It is apparent from the foregoing description that this inventionrelates to methods of protecting the internal surfaces of gun barrelsfrom frictional wear and chemical erosion comprising covering suchsurfaces with a layer of metal of the group consisting of tantalum,molybdenum, and tungsten. Gun barrels produced in accordance with thisinvention last longer and retain their accuracy longer than untreatedbarrels.

Variations and modifications of this invention as set forth in the abovedescription will become apparent to those skilled in the art. Forexample, a molybdenum, tantalum, or tungsten tube may be produced bydepositing a very thick layer of the given metal on a thin sleeve ofsteel and subsequently removing the steel by solution in strong acid.Such a tube of tantalum, molybdenum, or tungsten may be inserted intothe gun barrel as means of protection rather than coating directly uponthe bore surface itself.

What is claimed is:

1. A gun barrel comprising a basis metal of steel having a bore, themetal adjacent said bore being composed of an alloy of tantalum and thebasis metal, and a layer of tantalum covering said alloy to define thesurface of said bore.

2. A steel gun barrel having a bore surface alloyed with tantalum and anadherent layer of tantalum coating said alloyed surface.

References Cited in the file of this patent UNITED STATES PATENTS

2. A STEEL GUN BARREL HAVING A BORE SURFACE ALLOYED WITH TANTALUM AND ANADHERENT LAYER OF TANTALUM COATING SAID ALLOYED SURFACE.